warning: unexpected `cfg` condition value: `X`
  --> $DIR/compact-values.rs:11:28
   |
LL | #[cfg(target(os = "linux", pointer_width = "X"))]
   |                            ^^^^^^^^^^^^^^^^^^^
   |
   = note: expected values for `target_pointer_width` are: `16`, `32`, `64`
   = help: to expect this configuration use `--check-cfg=cfg(target_pointer_width, values("X"))`
   = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
   = note: `#[warn(unexpected_cfgs)]` on by default

warning: 1 warning emitted